Cone beam computer tomography (CBCT) assumes that the scanned object is static. When the object changes during scanning, this intra-scanning motion induces blurring and streak artefacts. These artefacts hamper image guided radiotherapy (IGRT) applications, as they reduce the success rate and accuracy of automatic registration techniques and hamper visual inspection.
For periodic motions, such as breathing, motion artefacts can be managed by respiratory correlated imaging techniques, i.e., exploiting the periodic feature of such motion through retrospective sorting of projection images into phase bins yielding four dimensional datasets. Non-periodic or sporadic motion (such as moving gas in the rectum) presents a difficulty.